1. Field of the Invention
This invention generally relates to oscillators, and more particularly, to an oscillator mounted on a mounting portion in which an oscillating portion has an insulating layer.
2. Description of the Related Art
Oscillators, in particular, voltage-controlled oscillators are for use in mobile communication terminals such as, for example, mobile telephones, Personal Handyphone Systems (PHS), wireless Local Area Networks (LAN), transceivers, and the like.
FIG. 1 is a circuit diagram showing a conventional oscillator. The oscillator includes an oscillating portion 11, and the oscillating portion 11 includes: a resonance circuit 20; an oscillating circuit 30; and a buffer circuit 40. A transistor Q1 included in the oscillating circuit 30 and a transistor Q2 included in the buffer circuit 40 are connected in a cascade connection.
The resonance circuit 20 is composed of: a variable-capacitance diode D1; capacitors C2 and C3; and a line S5 such as a stripline or the like. A control voltage Va to be applied to a control terminal Ta, after high-frequency component thereof is removed by a line S4 and a capacitor C1, is applied to the variable-capacitance diode D1. The capacitance of the variable-capacitance diode D1 is varied by the control voltage Va and the resonance frequency of the resonance circuit 20 is changed.
The oscillating circuit 30 is composed of a bipolar transistor Q1 and capacitors C5 and C6, and serves as a clap oscillating circuit, which is one type of Colpitts oscillating circuit. The base of the transistor Q1 is coupled through a coupling capacitor C4 to the resonance circuit 20.
The buffer circuit 40 includes a bipolar transistor Q2. The emitter of the bipolar transistor Q2 is connected to the collector of the transistor Q1 in the oscillating circuit 30, and the base of the transistor Q2 is coupled through a coupling capacitor C8 to the emitter of the transistor Q1.
A line S2 serves as an inductor for choke to remove alternating component, when the power is supplied from a power supply Vb to the collector of the transistor Q2. Resistors R1 through R4 determine how the transistors Q1 and Q2 are biased. Capacitors C7, C10, and C11 short-circuit the high-frequency component to ground.
Like the conventional oscillator of FIG. 1, the oscillator having the buffer circuit 40 therein includes the transistor Q2 and the like, thereby increasing the mounting area with a number of parts. The costs will also be increased. The oscillator that does not include the buffer circuit 40, however, has drawbacks in that the oscillation is not stable and the load change, higher harmonic level, and carrier to noise (C/N) ratio are not excellent.